Hard Drive Sander

Introduction: Hard Drive Sander

Many people have an old hard drive laying around. In this project we will put it to good use by turning it into a powerful disk sander! It's a cheap and easy project, but it has already proven to be very useful when sharpening tools and sanding though materials.

Make sure your harddrive has aluminium platters, and not glass ones. The glass platter might shatter and cause serious damage! How to check this?

Take a strong neodymium magnet and go over the platter. You should feel some resistance if it's an aluminium one (due to eddy currents)

Look at the sun though the harddrive. If you can slightly see the sun, it's glass.

To be completely sure: hold it in a vice, wear safety equipment (especially safety glasses!) and give it a slight hit with a hammer. If it shatters you shouldn't (and can't at this point :p) use it.

Step 2: Disassembly

The first step of the build is disassembling the harddrive. Simply remove all the screws; there will probably be one under the sticker as well.

Next, we'll need to take out the guts. Undo all the screws you see and remove the components. You might have to use some force to remove the magnets, but these are worth keeping!

Also remove the hard drives and spacers themselves, since we'll have to restack them.

Small bonus project

These strong magnets are ideal to make a magnetic parts tray. You can remove the protruding metal bits with a pair of pliers. They will break off quite easily, since they are quite brittle.

I had a lid of an old metal pen case, to which I attached the magnets; et voila!

Step 3: Wiring the Motor

The crucial step of this project is controlling the motor of the harddrive.

The motor inside a harddrive is a brushless DC motor (BLDC). They come in 2 variants: triangle and star topology. For the full explanation, take a look at the Wikipedia page, I will focus on the wiring.

A BLDC motor can easily be controlled by an Electronic Speed Controller (ESC), and while we could have made this ourselves, it's far easier and cheaper to buy a speed controller. Furthermore, they can easily be controlled by a servo tester; as the name implies, it is used to test servo motors. However, the type of control signal for a ESC and a servo are the same: it's a simple PWM signal. In case of the servo, this corresponds to a motor position; for the ESC it corresponds to a speed.

Let's focus on the wiring of the motor, depending on your harddrive you will have 1 of 2 types:

3 Pins

If your motor has 3 pins, it's triangle topology: there is a coil between every pair of pins. This is the easy case: just solder the 3 wires of the ESC (the blue ones) to the 3 pins of the motor (a,b,c on the diagram) and call it a day.

4 Pins

In case there are 4 pins on the motor, you have a star topology. We will need to connect the ESC to points a,b,c on the diagram. To do this, we have to identify to which 3 of the 4 pins they correspond. To achieve this, we'll have to bust out the multimeter and measure the resistance between the pins. As we can see on the picture, 3 combinations give a resistance of 1 Ohm, while 3 others give 2 Ohms. 1 Ohm is the resistance of 1 coil (1 of the Z's on the diagram), while the 2 Ohms is the resistance of 2 coils in series. Conclusion: the combinations where we measured 2 Ohms are the ones we need (a,b,c on the diagram)!

After soldering the ESC, mount it inside the hard drive case where the reading head was. Every harddrive is different, so try to find a way of attaching it securely; I just some scraps of aluminium, although glue would have also worked.

Attach 2 banana terminals to the red an black wires of the ESC. Drill 2 holes in the enclosure to mount them. You could also use a barrel jack if you want to use it with a 12 V wall adapter instead of a bench powersupply.

You can already connect the servo tester to the 3 pin connector of the ESC, plug the banana jacks into 12 V and give the motor a try. That's the electronics basically done!

Step 4: Enclosure

Now that our motor spins, we can turn it into a sander!

Start by taking a piece of sandpaper and cut out a circle that fits your hard drive platter. Attach it to the platter with double sided tape. This will allow us to easily replace it in the future.

My harddrive had 2 platters with some spacers in between. Put the spacers down first and then add the 2 platters on top of each other for extra strength. Screw it tightly in place, this bracket will also keep the sandpaper firmly in place (that's why we didn't glue the sandpaper).

The last thing is to cover up and protect the ESC and to make it more usable. Therefore, we will reinstall the original lid, with a cutout for the harddisk. Since the cover is very hard and reasonably thick steel, it is preferable to use a thin cutoff wheel on your rotary tool. Wear some kind of face protection and a breathing mask while doing this: it produces dust and the cutoff wheel can easily break and fly away!I also added an upright piece out of thin aluminium that seals off the side and glued it in place.

As a last step, attach the servo tester to the 3 pin connector of the ESC. I decided to leave it external, since there was not enough place inside the enclosure, and since it allows me to use it to test actual servo's when I'm not sanding.

Step 5: Test & Enjoy

We're done! The only thing left to do is to test our new hard drive sander. Connect the servo tester and plug it into a 12 V supply which can deliver about 1 A (see how I made one from an old ATX powersupply here, or a fancy digital one here). Make sure the servo tester is in manual mode and turn the knob, the sander should start spinning!

I hope you liked the project and have found a good use for that unused old hard drive!

Hello Thomas, Good to see you really make an effort to maintain and update your instructable, especially for safety issues. I'll vote for that part, but also for the elegance of using an esc instead of just leaving the PCBA to handle that.

There's 2 types of platters commonly used in HDDs. Glass and Aluminum. The glass shatters and obviously you should test what your platter is made of.But the aluminium is close to impossible the break. It's the coating on it that makes it so strong. Having just destroyed my 2300 HDD's last week for a customer, not one single alu-platter broke during onsite breaking of the HDD's. the Cast Housing breaks, metal top cover bends and the platter bends.Destroying the platters off-site after dismantling with a 15hp shredder only tears and rips the platters into mangled pieces. No breaking at all..Been doing Electronics Recycling for 19 years now, check if it's not glass and you're ok

From what I've read.it seems the smaller 2.5" laptop hd platters are more often than not made of glass while the larger desktop pc HD have aluminium platters. Either way best to be sure - applying pressure to a high speed spinning disc is not the time to find out it's made of potentially lethal glass.

Correct... Most 3.5" HDD's all still use aluminum, since it's less prone to breaking and easier to manufacture and has longer endurance, especially with high RPM drives (look for 15k HDD's that are used in server applications if you want really high speed sanding capabilities)

I have salvaged Hard drives from the old 8 inch to the small 2.25 laptop drives and never found a disk made of glass. All I found were aluminum that is coated with a thin film of platinum and ferromagnetic compounds. I never even heard about a glass platter. Maybe they were made in the beginning of hard drive manufacturing. Never too old to learn huh!

When you're running up the motor on a RC model, you always start from zero throttle then increase it. As you increase the throttle, the frequency sent to each winding increases, and the motor ramps up its speed. Maybe the motor just follows the frequency. Is there any feedback from the motor to the ESC to tell it the speed of the motor? There are only three wires. So if you tried to spin the motor initially with a frequency equivalent to running speed, it's quite possible the motor wouldn't turn.

To good to be true. Put three of these side by side and use them to sharpen blades. Check out "Stumpy Knubs" on the youtube. He has a mod of an existing sharpening station build in the same configuration as this sander but bigger. We're going to build tonight. Thanks and keep making

Even better, I could use that velcro like stuff they put on sanders today and then just switch the papers. Actually for the stones, I need diamond discs, but the ones I have are the velcro backed kind. I just saw the replacement hook papers in the hardware store. This is my very next project. You really got my creative ideas flowing with this one. Thanks.

I spent hours removing hard drives from computers that my wife's ex employer wanted the discs destroyed for security purposes, taking them apart and salvaging what I wanted. As I disassembled them I tried to figure out how to get the motors to turn but I had no luck. I couldn't find anything on YouTube to help either. I wish that I had had this instructable then, because I ended up recycling all of the cases after I removed the spindles and magnets from them.